Radio broadcasting system



Jan. 5 I 1,522,581

L. ESPENSCHIED RADIO BROADCASTING SYSTEM Filed Aug. 16, 1922 III IN V EN TOR.

' LZYyamc/u'ed ATTORNEY Patented Jan. 13, 1925.

UNITED STATES. PATENT on-Ice.

- LLoYn nsrnnsonmn, or norms, NEW YORK, ASISIGNOR 'ro AHERICAN TELEPHONE AND- 'rmEGmn COMPANY, A CORPORATION or NEW YORK.

mro .nnoanoas'rmo sysm.

Application fled Auguat m, 1822. Serial no. 582,257

To all whom it may concern:

Be it known that I, LLOYD Esrnnsonmn, residing at Hollis, in the county of Queens and State of New York, have invented certain Improvements in Radio Broadcasting Systems, of which the following is a specification.

This invention relates to a-radio telephone broadcasting system in which thereceiving stations are enabled to have a positive indication at all times, as to whether or not they are in .connection with and ready to receive from the central broadcasting station.-

The purpose of such an arrangement is to afford a broadcasting subscriber who may be sending out information of a business character or otherwise, a greater measure of assurance that the receiving stations to which he desires to transmit are actually receiving the information set out.v A second purpose is to give the subscriber at the receiving station definite information as to the condition of receptivity of the radio transmission channel. A break in this transmission channel may be due'tosome defect in the receiving station itself or some defect in the transmittin station, but in any case, it is desirable t at the receiving subscriber shall be notified as to the condition of the channel. Such assurance on the part of the broadcaster is especially needed in the case of emergency alarm services as, for example, when a broadcasting station may be employed to transmit fire alarms to a number of designated receiving stations, or where police information is broadcasted from a central station to a number of correlated pick-up points.

The invention briefly consists in sending out continuously carrier waves from the broadcasting station and employing these at each of the receiving stations to operate an indicator or alarm device; in other words,

to normally establish channels betweenthe' broadcasting station and all the receiving stations involved and to operate these channels on the closed circuit basis, whereby the receiving station always definitely knows, as by the holding up of a signal, that it is in proper connection with the central station. The invention will be better understood by reference to the accompanying drawing, in which the figure shows a transmitting station adapted for broadcasting purposes, and

a plurality of receiving stations adapted to cooperate with the broadcasting station. In the figure, represents the. transmitting antenna, including a variable condenser 6 and an inductance 7, with which latter is associated the local generating circuit. This circuit may take on a large variety of forms and the one shown is solely for illustrative purposes. As such, there is a generator 8 of high frequency oscillations. connected through a normally closed circuit to a mod ulating device 10'. A generator of speech signals to be transmitted and comprising a microphone 12, a battery 13 and a transformer 14 is also. associated with the modulator 10. The output of this modulator may then be associated with the transmitting antenna in any well known manner. such as by means of the coil 15. If desired, a wave filter 17 may be inserted to eliminate such frequencies as are not desired. As thus described, the transmitting station is adapted to emit continuously high frequency oscillations even' though no message may at the time be impressed from the microphone 12.

A plurality of receiving stations R R,, R, and R are shown, each of these being designed to be receptive to the waves sent out from thetransmitter. The details of these receiving stations may vary but all have the featurethat an indicating means is present, which is responsive to the carrier frequency received whether this carrier frequency be modulated or not. One form which the apparatus at the receiving station may take is shown at the receiver R in which a tuned circuit supplies the received oscillations to a detector 21, preferably of the thermionic type, the detected message from the modulated wave of the transmitter being then received in some device such as the telephone 23. Such a device is responsive only to the modulations of the transmitted wave but I propose to supply in addition apparatus which is responsive to the received waves, whether they are modulated or not. To this end, I make use in the specific apparatus shown at R,

of the peculiar characteristic Ofathermionic vacuum tube detector. In such a detector, the average spacecurrent flowing from the plate to filament changes as the amplitude of the received high frequency oscillations changes. In general, the average value of the space current is raised on the receipt of high frequency signals, although under cerage space current islindicated'by 'ia change.

in the currentfiowing through a "relay'25 which is connected-in series with-the output circuit of detector 21. If a signal is being "combination of-teeth thereon, and upon roreceived the space current throughthe relay 2?; is sufiicient to draw up its armature whichcloses a local circuit containing-an indicating device, such as a-lamp. If a break in the receipt of signals occurs, however, this space current drops to a sufficiently low value so thatthe armature is no longer held up and consequently the lamp indicator 27- -is extinguished. 'An alarm which will give a positive signal in case of non-receptivity is shown at 28, this being operated when the armature of relay 25 drops to its back contact. The operation of a detector with characteristics of this nature is more fullydescribed in my a plication, Serial No. 500,034, filed Septem er 12, 1921, and any of the modifications shown therein may obviously be applied in this invention.

A second form which the apparatus of the receiving station'may take is indicated at the receiver 3,, in which the locally tuned receiving circuit 31 has bridged across its condenser a detector 32, such as a crystal detector, and across this or in some other suitable manner may be connected the telephones 33. In case no signals are being re,

ceived, there is no current flowing through the detector 32. In case such signals are being received there is a rectified component of current present so that if a relay 35 is inserted in series with the detector and is shunted by the condenser 36 to give a free path for alternating current there will then flow through the relay 35 a steady current, the magnitude of which will depend on the amplitude of the received oscillations. This relay 35 is in turn adapted to maintain closed a circuit including an indicating device, such as the lamp 37. In case of failure to receive the high frequency oscillations, due to a defect at either the transmitting or receiving station, the local circuit will he opened and the. light 37 will he extinguished.

The relay 25 at station It, and the relay 35 at R are both :"lmv acting relays, so that they will not be. responsive to the rapid chan es in the amplitude of the received oscil ations which are present in case these received oscillations are modulated by a message to be transferred to telephone 23 or 33.

In case this system is to be used for such purposes as indicated aboove it may be desirable to have provision whereby the tramsend ,aoutselecting; current impulses from the transmitting station, making use of the carrier wave. 'At the transmittin station thereris shown-a code transmitter comprising, for example, a disc with a certain tation, 'adapted't-oclose a circuit comprising battery 40, relay 41,flcontact'42-and disc Upon being-energized, the relay 41 opens the circuit of-the oscillator 8, thus interrupting; the transmission of waves from the antenna iii-accordance with the code of the (i K,. "These breaks in the emission of the carrier wave produce corresponding m-- terruptions in the circuit controlled, forexample, by the relay 25 at station R, and thus may be used to control a selector 3,, which is responsive only to the code correspondingto the disc K,. On operation, this selector S may control anysuitable indicating device, such as a bell. Only those stations which are fitted with a corresponding selector S will respond to the call and obviously the various receiving stations may be grouped in any way desired, there being a corresponding disc for each group.

In case is desirable to make provision by which all of the receiving stations may be'called simultaneously, a. second disc K with a suitable code, may be connected with the transmitting station. At the receiver R, is shown a corresponding selective responsive device S,. An identical selective device would, in this case, be provided at each of the receiving stations.

If desired, the relay 26 may be made sufiiciently slow in its action so that the light 27 will not be responsive to the impulses coming from the discs K, or K which follow each other in rapid succession. The

light 27 will thus be extinguished only in I case the conditions for non-receipt of signals persist for a comparatively large element of time.

Numerous modifications may be made in this system in its various parts without dc parting from the spirit of this invention. For example, while I have described a simple form of selector mechanism. any system which operates in a substantially equivalent manner would be equally cti'ecti \e Reference may be made, for example. to my joint invention with Bown, disch d in application Serial No. 460,869., filed April 13, 1921. Also the control of the emission of oscillations may obviously he at. some other point of the circuit than in the leads from the oscillator 8 \Vhat is claimed is:

1. In a radio signaling system. a radiating station. means for transmitting carrier waves therefrom continuously, means for impressing thereon the message to be transmitted, a receiving station and means thereat for detecting the message to be transmitted, and supplemental means responsive to the umnmlulated component of the carrier wave to indicate suitable conditions for reception of the message impulses.

2. In a radio signaling system, a radiating station, means for transmitting carrier waves therefrom continuously, means for impressing thereon the message to be transmitted, a receiving station and means tliereat for detecting the message to be transmitted, supplemental means responsive to the. unmodutal'ed component of the carrier wave to indicate suitable conditions for reception of the message impulses, and a calling device Iii) at the transmitting station adapted to send impulses on the carrier wave to call the receiving station.

:3. In a radio signaling system, a radiating station, means for transmitting carrier waves therefrom continuously, means for impressing thereon the message to be transmit ted, a receiving station and means thereat for detecting the message to be transmitted, -supplemental means responsive to the unmodulated component of the carrier wave to indicate suitable conditions for reception of the message impulses, and. a call responsive device at the receiving station controlled thereby.

4-. In a radio signaling system, a radiating st at ion. means for transmitting carrier waves continuously, means for impressing thereon the message to be transmitted, a plurality of receiving stations. each adapted to be continuously responsive to said transmitted waves, means at each receiving station to indicate its condition of rcceptiveness, and a calling mechanism associated with the transmitter for calling all the receiving stations simultaneously.

5. In a radio signaling system, a radiating station, means for transmittingcarrierwaves continuously, means for impressing thereon the message to be transmitted, a plurality of receiving stations, each adapted to be continuously responsive, to said transmitted waves, means at each receiving station responsive to the unmodulated component of the carrier waves to indicate its condition of receptiveness, and a selective calling mechanism associated with the transmitter for calling certain receiving stations.

6. In a radio signaling system, a radiating station, means for transmitting carrier waves continuously, means for impressing thereon the message to be transmitted. a plurality of receiving stations, each adapted to be continuously responsive to said transmitted waves, means at each receiving station to indicate its condition of receptiveness, and a calling mechanism associated with the transmitter for selectively calling any group or for calling all of the receiving stations.

7. In a radio signaling system, a radiating station. means for transmitting carrier waves continuously, means for impressing thereon the message to be transmitted, a plurality of receiving stations, each adapted to l) continuously responsive to said transmitted waves, means at each receiving station responsive to the unmodnlated component of the carrier waves to indicate its condition of receptiveness, a selective calling mechanism associated with the transmitter. for calling certain receiving stations, and a selective responsive device at the receiving station responsive to certain signals only.

8.\. In a radio signaling system. a radiating station, means for transmitting carrier waves continuously, means for impressing thereon the message to be transmitted, a plurality of receiving stations, each adapted to be continuously responsive to said transmitted waves, means at each receiving station for receiving a transmitted message and other means responsive to the unmodulated component of the carrier waves to indicate its condition of receptiveness, a selective calling mechanism associated with the transmitter for calling certain. receiving stations.

Intestimony whereof, I have signed my name to this specification this 14th day of August 1922.

LLOYD ESPENSCHIED. 

